1. Technical Field
The present invention relates generally to mobile-to-mobile telecommunications and in particular to delivering calls from an originating mobile switching center (MSC-O) to a called mobile's voice mailbox. Still more particularly, the present invention relates to employing existing message definitions to obtain a temporary local directory number (TLDN) to facilitate call delivery from the MSC-O to the called mobile's voice mailbox.
2. Description of the Related Art
Mobile service subscribers may currently obtain both "roaming" access, or wireless service outside a home service area, in addition to many other services including incoming call redirection to voice mail. When a call attempts to terminate to a mobile, the home mobile switching center (MSC-H) handles the call and, if necessary, redirects the call to the serving mobile switching center (MSC-S) in a process known as call delivery. In the event that the called mobile cannot or does not accept the incoming call, the MSC-S may request, via signaling messages that the MSC-H redirect the incoming call to the called mobile's voice mailbox. Generally, the MSC-H will have a direct connect trunks to the voice mail system, thereby allowing a non-PSTN routable numbers to be used as the redirection number to steer the redirected call to the called mobile's voice mailbox. For example, the redirection number used for voice mail could be `#4258675555`. Since the use of such non-PSTN routable numbers requires special digit translations understood only by the MSC-H, all calls to a mobile must first route to the mobile's MSC-H before call delivery occurs to the MSC-S. This ensures that the MSC-H can redirect the call to the called mobile's voice mailbox if necessary.
For reasons described in the paragraph above, mobile-to-mobile calls must also first route the called mobile's MSC-H. The originating mobile switching center (MSC-O) serving the originating mobile cannot redirect the call to the called mobile's voice mailbox based on a non-PSTN routable number. When the mobile switching center serving the called mobile (MSC-S) determines that call redirection to voice mail is required, a request to invoke redirection to voice mail is signaled to the MSC-H. In the ANSI-41 wireless networking standard, this message is the Redirection Request (REDREQ) message; other wireless networking standards such as the Mobile Application Part signaling used for GSM networks implement a similar mechanism to redirect incoming calls to voice mail.
The mechanism described above incurs substantial use of trunk resources. A call must be connected from the MSC-O serving the originating mobile to the called mobile's MSC-H and thence to the MSC-S serving the called mobile. A mobile in Seattle, Wash. calling Dallas-based mobile that happens roaming in Portland, Ore. involves a trunk from the Seattle MSC-O to the Dallas MSC-H and thence to the Portland MSC-S rather than routing directly from Seattle to Portland. The indirect routing through Dallas is required in order to ensure that the call can be redirected by the Dallas MSC-H to voice mail if requested by the Portland MSC-S. In addition to wasteful use of trunk resources, this type of call routing increases voice transmission delay which may be detrimental to perceived audio quality. Some MSC's implement digital mobile voice coder bypass techniques in which digitally encoded speech may be passed directly from mobile to mobile provided that the bit patterns not be altered by transmission equipment. Since long-haul trunks require echo cancellation equipment, such voice coder bypass techniques will not operate on long-haul trunk circuits, causing voice quality degradation because the MSC-O must decode the digitally compressed voice signal and then the MSC-S must re-encode and digitally recompress the voice signal.